For a Long Term Evolution (LTE) system, packet data is transmitted on an Orthogonal Frequency Division Multiplexing (OFDM) basis. When cells are networked at an identical frequency, it is required to carry out power control so as to prevent too strong interference among the cells.
Depending on whether or not transmission power is determined by a transmitter or a receiver, the power control may include open-loop power control and closed-loop power control. For the open-loop power control, the transmitter determines its transmission power based on its understanding of channels. An advantage of the open-loop power control is that no additional signaling overhead is required, and a disadvantage is that there usually exists a difference between the transmitter's understanding of the channels and the actual situation of the channels, so the open-loop power control based on the inaccurate understanding of the channels is usually inaccurate. For the closed-loop power control, the receiver determines the transmission power of the transmitter. An advantage of the closed-loop power control is that the receiver may determine the transmission power of the transmitter in accordance with the actual received signal quality, so it is able to accurately adjust the power. A disadvantage thereof is that additional signaling overhead is required.
As specified in the Standard, transmission power PPUSCH for one OFDM symbol of a Physical Uplink Shared Channel (PUSCH) transmitted by a User Equipment (UE) in subframe i may be calculated by the following equation:
            P      PUSCH        ⁡          (      i      )        =      min    ⁢                            {                                    P              CMAX                        ,                                                            10                  ⁢                                                            log                      10                                        ⁡                                          (                                                                        M                          PUSCH                                                ⁡                                                  (                          i                          )                                                                    )                                                                                        ︸                                      Bandwidth                    ⁢                                                                                  ⁢                    Factor                                                              +                                                                                          P                      O_PUSCH                                        ⁢                                          (                      j                      )                                                        +                                                            α                      ⁡                                              (                        j                        )                                                              ·                    PL                                                                    ︸                                      Substantial                    ⁢                                                                                  ⁢                    Open                    ⁢                                          -                                        ⁢                    Loop                    ⁢                                                                                  ⁢                    Operating                    ⁢                                                                                  ⁢                    Point                                                              +                                                                                          Δ                      TF                                        ⁢                                          (                      i                      )                                                        +                                      f                    ⁡                                          (                      i                      )                                                                                        ︸                                      Close                    ⁢                                          -                                        ⁢                    Loop                    ⁢                                                                                  ⁢                    Portion                                                                                }                ⁡                  [          dBm          ]                    .      
PCMAX denotes allowable maximum transmission power of the UE. MPUSCH(i) denotes a bandwidth allocated by an ith subframe for PUSCH and is represented by the number of Physical Resource Blocks (PRBs). PO_PUSCH(j) is equal to a sum of an 8-bit cell-dedicated normalization portion PO_NOMINAL_PUSCH(j) and a 4-bit UE-dedicated portion PO_UE_PUSCH(j). PO_NOMINAL_PUSCH(j) (j=0 or 1) and PO_UE_PUSCH(j) (j=0 or 1) are configured by a Radio Resource Control (RRC) layer. When a resource used by PUSCH initial transmission/retransmission is a Semi-Persistent Scheduling Uplink-grant (SPS UL-grant), j=0, and when the resource used by PUSCH initial transmission/retransmission is a dynamical scheduling UL-grant, j=1. In other words, two different sets of power control parameters are used for the dynamical scheduling PUSCH and the persistent scheduling PUSCH, and are configured by different Information Elements (IEs) of the RRC layer, respectively. For the retransmission or initial transmission of a random access message3 (MSG3), j=2, and at this time, PO_UE_PUSCH(2)=0 and PO_NOMINAL_PUSCH(2)=PO_PRE+ΔPREAMBLE_Msg3, PO_PRE and ΔPREAMBLE_Msg3 are both configured by the RRC layer. α(j) denotes a power compensation factor. When j=0 or 1, αε{0, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1}, i.e., α(j) is a 3-bit cell-level parameter and configured by RRC layer signaling, and when j=2, α(j)=1. PL (Path Loss) denotes a downlink path loss detected by the UE in a unit of dB. PL=referenceSignalPower−higher layer filtered RSRP, where ReferenceSignalPower is configured by the RRC layer. ΔTF(i) denotes a transmission format gain for indicating whether or not to adjust transmission Power Spectrum Density (PSD) in accordance with different Modulation and Coding Scheme (MCS) levels. When KS=1.25, ΔTF(i)=10 log10((2MPR·KS−1)βoffsetPUSCH), and when KS=0, ΔTF(i)=0, where KS is a UE-dedicated parameter and indicated by RRC signaling deltaMCS-Enabled. In addition, in the above equation, when the data transmitted via PUSCH merely contains control data other than Uplink-Synchronization Channel (UL-SCH) data, MPR=OCQI/NRE, and in the other cases,
      MPR    =                  ∑                  r          =          0                          C          -          1                    ⁢                          ⁢                        K          r                /                  N          RE                      ,where C denotes the number of code blocks, Kr denotes a length of an rth code block, OCQI denotes the number of bits in downlink Channel Quality Indication (CQI) containing Cyclic Redundancy Check (CRC) bits, and NRE denotes the total number of Resource Elements (REs) and it is defined as NRE=MscPUSCH-initial·NsymbPUSCH·initial. where C, Kr, MscPUSCH-initial and NsymbPUSCH·initial have been defined in 3GPP Release 36.212, and C, Kr and MscPUSCH-initial may be obtained from a Physical Downlink Control Channel (PDCCH) for the initial transmission of transport blocks.
When the data transmitted via PUSCH merely contains the control data other than UL-SCH data, βoffsetPUSCH=βoffsetCQI, and in the other cases, βoffsetPUSCH=1. f(i) gives a state of the current PUSCH power to be controlled and adjusted, and it is defined as follows.
1. When the power control in a accumulated mode is enabled by the UE-dedicated parameter notified via the RRC layer, i.e., Accumulation-enabled, or when a Transmitter Power Control (TPC) command field δPUSCH is contained in Downlink Control Information (DCI) Format0 and the CRC bits use PDCCH scrambled by a Cell Radio Network Temporary Identifier (Temporary C-RNTI), f(i)=f(i−1)+δPUSCH(i−KPUSCH), where δPUSCH(i−KPUSCH) denotes a TPC command transmitted by DCI Format0 or Format3/3A on an (i−KPUSCH)th subframe, and f(0) denotes an initial value after f(i) is reset.
For Frequency Division Duplex (FDD UL/DL), KPUSCH=4. For Time Division Duplex UpLink/DownLink (TDD UL/DL) configurations 1-6, the values of KPUSCH are shown in Table 1. For TDD UL/DL configuration 0, when the PUSCH transmission scheduled by PDCCH DCI Format0 occurs in subframe 2 or 7, and the least significant bit of a UL index information field in DCI is 1, KPUSCH=7. For the PUSCH transmission in the other cases, the values of KPUSCH are shown in Table 1.
The UE tries to decode PDCCH of DCI Format0 using its C-RNTI or Semi-Persistent Scheduling-Radio Network Temporary Identifier (SPS-RNTI) at each Discontinuous Reception (DRX) subframe, and also tries to decode PDCCH of DCI Format3/3A using its Transmitter Power Control-Physical Uplink Shared Channel-Radio Network Temporary Identifier (TPC-PUSCH-RNTI).
When both PDCCHs of DCI Format0 and DCI Format3/3A are detected by the UE simultaneously within an identical subframe, the TPC command δPUSCH from DCI Format0 is merely used by the UE. When no TPC command is decoded from a certain subframe, or the UE is in a DRX state, or the ith subframe in a TDD mode is not an uplink subframe, δPUSCH=0 dB. When an accumulated modified value δPUSCH dB is contained in PDCCH of DCI Format0, its adjusted values are shown in Table 2. However, when DCI Format0 has a function of SPS activation or SPS releasing, δPUSCH=0 dB. When the accumulated modified value δPUSCH dB is contained in PDCCH of DCI Format3/3A, there are two sets of the adjusted values, i.e., Set 1 shown in Table 2, and Set 2 shown in Table 3. The set of the adjusted values may be determined in accordance with the number of bits of the RRC layer parameter, i.e. TPC-Index.
When the UE has reached the maximum transmission power, the “positive” TPC commands cannot be accumulated, and when the UE has reached the minimum transmission power, the “negative” TPC commands cannot be accumulated. In addition, the accumulation of the TPC commands is required to be reset by the UE when PO_UE_PUSCH is changed or when a random access response message is received (the UE is in a synchronous/re-synchronous state).
2. When the accumulated mode is not enabled through the UE-dedicated parameter configured by the RRC layer, i.e., Accumulation-enabled, UE is in an absolute closed-loop mode and f(i)=δPUSCH(i−KPUSCH), where δPUSCH(i−KPUSCH) is indicated by PDCCH of DCI Format0 in an (i−KPUSCH)th subframe. The values of KPUSCH may be determined as follows. For FDD, KPUSCH=4. For TDD UL/DL configurations 1-6, the values of KPUSCH are shown in Table 1. For TDD UL/DL configuration 0, when the PUSCH transmission scheduled by PDCCH of DCI Format0 occurs in subframe 2 or 7 and the least significant bit of the UL index information field in DCI is 1, KPUSCH=7, and for the PUSCH transmission in the other cases, the values of KPUSCH are shown in Table 1.
In the absolute mode, δPUSCH is indicated by PDCCH of DCI Format0, and its values are shown in Table 2. When DCI Format0 has a function of SPS activation or SPS releasing, δPUSCH=0 dB. When PDCCH of DCI Format0 is not decoded from a certain subframe, or UE is in the DRX state, or the ith subframe in the TDD mode is not an uplink subframe, f(i)=f(i−1).
3. In methods for calculating the two TPC adjusted values f(*) (in the accumulated mode or the absolute mode), the initial value is set as follows.
When PO_UE_PUSCH is changed, f(i)=0, and otherwise, f(0)=ΔPrampup+δmsg2. δmsg2 denotes the TPC command field indicated in the random access response message, as shown in Table 4, and ΔPrampup is configured by the RRC layer and corresponds to a total power increment between the initial transmission and the last transmission of Preamble.
TABLE 1Values of KPUSCH for different TDD UL/DL configurationsTDD UL/DLsubframe number iConfiguration01234567890——674——6741——64———64—2——4————4——3——444—————4——44——————5——4———————6——775——77—
TABLE 2Meanings of TPC command fields in DCI Format 0/3TPC Command Absolute δPUSCH Field inAccumulated[dB] only DCIDCI format 0/3δPUSCH [dB]format 00−1−410−1211334
TABLE 3Meanings of TPC command fields in DCI Format 3ATPC Command Field inDCI format 3AδPUSCH [dB]0−111
TABLE 4TPC command field δmsg2 of PUSCH for schedulingTPC CommandValue (in dB)0−61−42−23042546678
Meanwhile, as specified in the Standard, Overload Indicator (OI) information is interacted via an X2 interface. The parameter OI is used to indicate which PRBs of an adjacent cell are strongly interfered. There are three levels for an OI report, and each PRB is represented by two bits, with a minimum update time of 20 ms.
In the equation for calculating the transmission power of uplink PUSCH, the parameters PCMAX, PO_PUSCH(j), α(j), ΔTF(i) and f(i) are configured by a base station, and the parameter MPUSCH(i) is determined by scheduling. UE merely takes charge of measuring the downlink path loss PLDL, andthe base station takes charge of determining PO_PUSCH(j), α(j), ΔTF(i) and f(i). The algorithm for the uplink PUSCH power control actually includes the setting of an open-look operating point and an algorithm for the closed-loop power control, and a target Signal to Interference plus Noise Ratio (SINR) is required when determining f(i).
The target SINR for the existing uplink PUSCH power control is determined by theoretical calculation. Presumed that KS=0, then ΔTF(i)=0, and at this time, the target SINR may be set as follows.
The target SINR desired at an eNB side may be represented as SINRtarget=(PO_PUSCH(j)+α(j)·PL+f(i)−PL)−(I+N). The uplink loss PL is a difference between uplink transmission power and uplink reception power of the UE, i.e., PL=PTX−PRX. The uplink reception power PRX of the UE may be measured at the base station, and the uplink transmission power PTX of the UE may be obtained by Power Headroom Report (PHR) using the following equations:PH(i)=PCMAX−{10 log10(MPUSCH(i))+PO_PUSCH(j)+α(j)·PL+ΔTF(i)+f(i)} [dB], and
      P    TX    =      {                                                                      P                CMAX                            -                              PH                ⁡                                  (                  i                  )                                                                                                        PH                ⁡                                  (                  i                  )                                            >              0                                                                          P              CMAX                                                                          PH                ⁡                                  (                  i                  )                                            ≤              0                                          .      Total uplink interference I+N may be represented as I+N=(−174 dBm/Hz+10*lg(180 kHz)+NoiseFigureup)+IoTup. NoiseFigureup denotes a noise index and it usually has a value of 7. IoTup denotes an interference margin for each PRB, and it is used to control the interference of a current cell on an adjacent cell. Currently, this parameter is set as a constant value or set in accordance with IoT measured by the base station in real time.
As can be seen from the above, merely the fixed interference or the real-time interference measured by the base station, rather than the interference between the adjacent cells, is taken into consideration for the current uplink PUSCH power control. The method for the power control in accordance with the fixed interference is simple, but it is impossible to be applied to different scenarios. For the method for the power control in accordance with the real-time interference measured by the base station, the information interaction between the base stations is not required. However, when the interference of an adjacent cell on a current cell is too strong or weak, the power of the current cell is increased or decreased, which thus results in too strong or weak interference on the adjacent cell. At this time, the power of the adjacent cell is increased or decreased, which in turn results in too strong or weak interference on the current cell. Due to such a vicious circle, the system interference is unstable, i.e., it may be increased or decreased gradually, so the system performance may be adversely affected, especially for cell-edge users.